iptables duplicate port traffic

I want to clone/duplicate all udp traffic incoming on port 8500 to port 8600. It is important that the source address is not modified. Also both ports must be accessible by applications (the packets must still arrive on the original port). This solution (https://unix.stackexchange.com/questions/704887/nftables-duplicate-udp-packets-for-specific-destination-ipport-to-a-second-d) does work on a newer system, unfortunately the machine in question is running kernel 3.10 on RHEL 7 and I am not allowed to update it.